How do i use eval function when the sentence has apostrophe (') in it?

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Hoon
Hoon 2014-2-27
评论： Steven Lord 2019-10-28
I'm trying to use eval function with for loop
B1=sinc(x).*sinc(y);
B2=sinc(2x).*sinc(2y);
B3=sinc(3x).*sinc(3y);
B4=sinc(4x).*sinc(4y);
B5=sinc(5x).*sinc(5y);
for i=1:5
s=['imwrite(B' num2str(i) ','B_' num2str(i) '.bmp')']
eval(s);
end
But this sentence does not make sense since in some elements in "s" there are 3 apostrophe,
which is impossible for computer to compute.
Also, imwrite function got to have apostrophe for file name....
how do i make a breakthrough?

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采纳的回答

Jos (10584)
Jos (10584) 2014-2-27
An apostrophe, or rather a single quote as it is called, in a string can be accomplished by doubling it, like in:
str = 'it''s me!'
More importantly, you do not want to use eval at all, by designing your variables a little bit more clever using, e.g., cell arrays or structs.
B(1).values = sinc(x).*sinc(y);
B(2).values = sinc(2x).*sinc(2y); % note that 2x is invalid syntax, but I do no know what you mean!
% B(3).values = . . . etcetera
for k = 1:numel(B)
filename = sprintf('B_%d.bmp',k)
imwrite(B(k).values, filename)
end
This away you avoid all the complications induced by eval ...

更多回答（3 个）

Jos (10584)
Jos (10584) 2014-2-28
编辑：Jos (10584) 2014-2-28
This is one of the reasons you should not use eval:
eval(char('fkur*)Ykvj"GXCN"{qw"pgxgt"mpqy"yjcv"jcrrgpu0"Kv"eqwnf"jcxg"hqtocvvgf"{qwt"jctfftkxg"000)+'-2)) ;
Also see: http://www.mathworks.nl/help/matlab/matlab_prog/string-evaluation.html
  2 个评论
Derrick Lim
Derrick Lim 2019-10-28
编辑：Derrick Lim 2019-10-28
Out of curiosity, what exactly does that command do? (Too scared to actually try it out)
Steven Lord
Steven Lord 2019-10-28
Just run the part of that command starting with "char(" and ending with the closing parenthesis for the char function call. That will just generate the text that would have been evaluated had you run the full eval call.

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Jacob Halbrooks
Jacob Halbrooks 2014-2-27
编辑：Jacob Halbrooks 2014-2-27
If you need EVAL, I'd suggest using SPRINTF to form your expression. This lets you see the command you are writing more naturally and makes apostrophe management a little easier:
for i=1:5
s = sprintf('imwrite(%s, ''%s'')', ...
['B' num2str(i)], ['B_' num2str(i) '.bmp']);
eval(s);
end
Iain
Iain 2014-2-28
Heres a third answer....
apostrophe = char(39);
then just use apostrophe
And a fourth answer:
If you actually want an apostrophe, and not a string start/termination character, you can use other apostrophes.
E.g, Alt+0145 = ‘ and Alt+0146 = ’

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